Under a sunny outdoor backlight photographing condition or the like, a range of a subject brightness in a photographed scene (hereinafter referred to merely as a “brightness range”) becomes wider. When a subject with a wider brightness range is photographed by a digital camera, the brightness range might not be contained in a dynamic range recordable in an image pickup system and an image signal processing system. In that case, in a dark section in the image, so-called blocked-up shadows occur, that is, the image is underexposed. In a bright section in the image, on the contrary, blown-out highlights occur, that is, the image is overexposed.
Technologies for solving such phenomena include a High Dynamic Range Imaging technology (hereinafter referred to as HDR technology). In the HDR technology, the same photographed scene is photographed plural times while a shutter speed is changed every time, and a plurality of images with exposure amounts different from each other (hereinafter referred to as differently exposed image) are obtained. A pixel value of image data obtained with a larger exposure amount is used for a region where blocked-up shadows might occur in the image, while a pixel value of the image data with smaller exposure amount is used for a region where blown-out highlights might occur, and synthesis processing is performed. As a result, an image in which gradation from a dark section to a bright section in the image is reproduced can be obtained.
In JP07-75026, an exposure amount to an image pickup element is changed in different n stages (n is an integer not less than 2), and an article is photographed. Image data in n sets are photographed with each exposure amount in n stages and obtained from the image pickup element. Two image data obtained with adjacent exposure amounts are synthesized and become a synthesized image having an expanded dynamic range. The similar procedure is repeated for the remaining (n−1) sets of image data, and one image data is obtained in the end.
In JP2002-135648, photographing sessions are performed with a plurality of different exposure conditions before main photographing, information relating to the dynamic range of the photographed scene is obtained, and the exposure condition for the plural sessions of exposure in the main photographing is determined.
In JP2009-284136, an electronic camera capable of operating in a live-view mode determines a first exposure amount suitable for image pickup of a first region and a second exposure amount suitable for image pickup of a second region other than the first region if there is a first region exceeding the dynamic range of an imaging section in the live-view image. When a release button is pressed, the electronic camera takes a first image with the first exposure amount and a second image with the second exposure amount, respectively, reads out the second image by partial reading and synthesizes the first image and the second image.